This application claims the priority benefit of Taiwan application serial no. 91116951, filed Jul. 30, 2002.
1. Field of the Invention
The invention relates in general to a data modulating/demodulating method and a system and an apparatus using the same, and more particular, to a data modulating/demodulating method and a system and an apparatus using the same, in which a lookup table with reduced bit number is used, such that the processing efficiency is greatly enhanced, and the implementation cost is significantly reduced.
2. Related Art of the Invention
In a hard disc or optical disc system, Inter-Symbol Interference (ISI) effect frequently occurs for accessing data recorded in the disc, due to bandwidth limitation of the recording channel. To reliably access data under the effect of ISI, the channel bit modulation is performed on the data to be recorded. Before being recorded to the disc, the data to be recorded is converted into channel bit data in a format having the property of run-length limit (RLL). Referring to FIG. 1, a data byte is converted into channel bits after channel bit modulation.
The conventional channel bit modulation process for processing run-length limit data format is shown in FIG. 2, such as the EFM modulation for CD (Compact Disc) application and EFM+ modulation for DVD (Digital Versatile Disc) application. A source data signal 22 with a length of M bits, called a data symbol, is received. After the conversion by the run-length limit modulation table, a channel bit signal 24 with a length of N bits, called a codeword, is output and recorded in the recording channel 25. An example of the recording channel 25 is the storage space of a optical disc. For the application of DVD, the EFM+ (Eight-to-Fourteen Modulation plus) modulation method is adapted, which converts one 8-bit source data into 16 channel bits
To read the recorded data, it requires a channel-bit modulation to demodulate the recorded channel bits to the source data. As shown in FIG. 2, the data recorded in the recording channel 25 is read as the channel bit signal 26. Using the demodulation table 27, the channel bit signal 26 with a length of N bits, said a codeword, is converted into the data 28 with the length of M bits. The above modulation and demodulation conversion, such as EFM and EFM+, are normally achieved by looking up the conversion tables. Therefore, a modulation table with M bits(table entries) times N bits(data), and a demodulation table with N bits(table entries) times M bits(data) are required. The modulation table and the demodulation table thus occupy a relative large chip area and are costly.
The present invention provides a data modulating method to modulate a source data signal into a modulation signal. The source data signal is converted into a plurality of source conversion data with a first bit length. A data conversion step is performed to extend the source conversion data into a modulation signal assembled by a plurality of modulation data units with a second bit length. The first bit length is shorter than the second bit length, while the first bit length is determined according to data characteristic of the modulation data units.
The present invention provides a data modulation apparatus including a modulation unit and an extension unit. The modulation unit receives a source data signal and converts such source data signal into a plurality of source conversion data with a first bit length. The extension unit extends the source conversion data into a modulation signal composed of a plurality of modulation data units with a second bit length. The first bit length is shorter than the second bit length, while the first bit length is determined according to data characteristics of the modulation data units.
The present invention provides a data demodulation method to demodulate a modulation signal into a data signal. The signal to be demodulated is partitioned into a plurality of partitions with a first bit length. According to a data conversion step, the partitions are folded into a plurality of modulation conversion data with a second bit length. The first bit length is larger than the second bit length, and the second bit length is determined according to data characteristics of the partitions of the demodulation signal. According to a demodulation table, the modulation conversion data are converted into the data signal.
The present invention further comprises a data decoding apparatus including a folding apparatus and a decoding unit. The folding apparatus receives a decoding signal and partitions the decoding signal into a plurality of partitions with a first bit length. According to a data conversion step, all the partitions are folded into a plurality of demodulation conversion data with a second bit length to be output. The first bit length is larger than the second bit length, and the second bit length is determined according to characteristics of the partitions of the demodulation signal. The demodulation unit converts the demodulation data into a data signal using a demodulation conversion table.